Every garden pond has sludge. It’s part of the natural balance of pond life to form a layer of dark, thick gunk on the pond floor and most of the time it’s nothing to worry about; but when ignored it can prove fatal to plants, fish and other wildlife or, at the very least, make your garden smell like rotten eggs.
Even with the best will in the world and a lot of spare time, you can’t stop things falling in your pond. Leaves from overhanging trees, bird droppings, and plant cuttings are all going to end up in there. All this, added to the matter already in your pond, sinks to the bottom and forms the layer of sludge. The sludge is a mixture of organic and inorganic matter which is mostly biodegradable in the right environment.
Now, a small layer of sludge isn’t anything to phone home about, but when it starts to build up and is left untreated it starts to starve the pond of oxygen. This lack of oxygen causes increased activity in anaerobic bacteria (the bad kind), which in turn produces hydrogen sulfide. Hydrogen sulfide is best known for producing a foul, rotting egg smell but it can also be toxic to fish and plants in large doses.
Not only can it kill plants and wildlife, it can also kill off the aerobic bacteria which eats the pond sludge. Unfortunately, this creates a vicious cycle where the pond sludge increases, the hydrogen sulfide increases with it, and the pond becomes more toxic. Here’s the process simplified –
How to fix it
It might seem like an obvious suggestion but the first step is prevention. Do everything you can to avoid organic matter falling into your pond –
- Keep bushes, trees and plants trimmed so there isn’t much overhanging
- Clean your pond regularly with a net to get out any floating debris.
- Use a bird deterrent (scarecrow etc) so they aren’t as prevalent.
- Keep a net over the pond to stop any larger debris getting in.
The second step is to physically clean out as much sludge as you can. Arguably the easiest way to do this, in a small pond, is by shoving a (gloved) hand in and pulling it out, but you can also use a net or pond vacuum. Admittedly, I’ve never used a pond vacuum but I have heard mixed reviews. Some people complain that it can suck up any smaller pond life (tadpoles etc) but you’ll have to use your own better judgement on that one.
The final step is to add to the aerobic bacteria in the pond. There are a few products out on the market including our own Envii Sludge Klear! By adding to the aerobic bacteria, you are increasing the rate at which the sludge is being eaten. Not only will this help with sludge but it will also improve the environment for fish and plants. It also contains facultative bacteria which break up the sludge, allowing the filter to consume it easier. Sludge Klear also works as low as 4°C which means you can use it through the winter and avoid the inevitable build up in early spring.